Television image projection system



April 1946 H. P. PROSSER 9 TELEVISION IMAGE PROJECTION SYSTEM Filedsept. 19, 1944 2 Shets-Sheet 1 INVENTEIR April 23, 1946. PROSSER 2,398,959

TELEVISION IMAGE PROJECTION SYSTEM I Filed Sept". 19, 1944 Q 2 Sheets-Sheet 2 INVENTEIR' Patented Apr. 23, 1946 UNITED STATES PATENT OFFICE TELEVISION IMAGE PROJECTION SYSTEM Harold P. Prosser, Mount Vernon, N. Y. Application September 19, 1944, Serial No. 554,786

This invention relates to television image prozclalms.

jection systems employing projection tubes of the cathode ray type and particularly to systems employing projection tubes utilizing the transprojection method whereby the light beam is modulated by passing it through a light relay screen positioned within the tube.

Due to the fact that both the light producing means and the electron gun structure are commonly positioned facing one side of the light modulating screen in a system of this type, it has heretofore been necessary to position the members so that the optical axis of either one or the other is obliquely incident with respect to the plane of the modulating screen. In so doing. un-

' desirable defects result in the projected image which has heretofore been unavoidable due to this characteristic. Uneven distribution of light resulting in the projected image when the optical axis of the light beam is obliquely incident with respect to the plane of the modulating screen, and image and frame distortion resulting when the scanning optical axis is obliquely incident with respect to the plane of the screen. It being necessary to provide electrical compensator means in the scanning control circuits in the latter case. The present invention deals primarily with this and other problems which the hereinafter description renders evident and although described in conjunction with a projection system employing the light polarization method of light modulation, the invention is obviously suited for application employingother methods of light modulation. g

The ideal form of a projection system 'of this type would be to provide means whereby the scanning beam may be positioned optically coaxial with respect to the projected light beam and perpendicular with respect to the plane of the light modulating screen. One form of a solution to the problem and the object of the invention may be set forth a following: An'assembly of light opticalmembers associated with an annular source of light provided in the system to operate in conjunction with a projection tube of the oath ode ray type having a modulating screen with light transmission characteristics and an electron gun structure positioned so that the scanning optical axis is centrally and perpendicular with respect to the plane of the modulating screen. The light optical members which are associated with the annular light source include an annular light reflector, an annular light condensing lens and a light deflecting member which is in the .form of a frustum of a cone. The members associated with the annular light source are positioned to circumscribe the optical axis of the tube and in close proximity of the gun structure. The light rays are directed from the annular source by the annular reflector to the annular condensing lens and thereby focused upon the deflecting face of the deflecting member and due to the rotary deflecting face thereof the light rays directed from the light source are deflected on a substantially common plane in the form of a light beam toward the modulating screen and I optically coaxial with respect to the scanning beam.

When employing the light polarization method of light modulation, crossed polarizing screens are disposed in the path of the light beam, one before the light strikes the modulating screen to polarize the beam and the other after the modulating screen and as familiar to those skilled in the art the plane of polarization of the beam passing through the modulating screen is caused to rotate in varying degrees in accordance with the elemental light and dark areas of the picture by electro-static charges impressed upon the face of the modulating screen by the electron scanning beam. The intelligence of the picture then filters through the second crossed polarizer and projected upon an observation screen by a suitable projection lens in image form with the defects as earlier defined eliminated.

The invention may be best understood by referring to the drawings, wherein like characters represent like members and wherein:

Fig. 1 is a plan view ofa television image projection system showing the light optical members and their arrangement in accordance with the invention, the light deflecting member positioned internally of the tube. I

Fig. 2 is a plan view similar to Fig. 1 showing the light deflecting member positioned externally of the tube. I i

Fig. 3 is a plan view of the light optical members showing their disposition in relation to a section taken across the neck of the tube in Fig. 1 with the light deflecting member positioned in.- temally of the tube.

Fig. 4 is a plan view similar to Fig. '3 showing relation of the light optical members to a section taken across the neck of the tube in Fig. 2, the

deflecting member positioned externally.

Referring to the drawings more in detail and to Fig. l, a television receiving tube l is shown which includes a modulating screen 2 having light transmission properties adapted to be scanned by a beamof electrons 3 on one side. A sun which is associated an annular reflector l and an annular condensing lens 8 circumscribing the go 0 having a deflecting face Iii in the form of a neck of the tube l and likewise the optical axis 5 positioned in close proximity to the head. of the gun structure 4; A light deflecting member frustum of a cone positioned within the tube l to deflect the light rays directed from .the source 8 in the form of a light beam-to the modulating screen 2 on a plane substantially perpendicular to the plane of the modulating screen. If deflecting plates X and Y are employed for deflection of the electron beam 3, the light deflecting member 9 is positioned directly in front of the plates X and Y. If other means of deflection of the electron beam is employed, the light deflecting member 9 may be positioned directly in front of the gun structure 4. The opening ll through the central portion of the deflecting member 9 being sufilciently large as to permit free action of the scanning electron beam 3 passing through to the modulating screen 2. j} polarizing screen l2 also positioned within the tube I and disposed in the path of the light beam after it is deflected from the member 9 to polarize the light passing through. The polarizing screen l2 positioned closely adjacent to the deflecting member 9 and also having an opening through the central portion sufliciently large as to permit free action of the scanning beam 3. A second polarizing screen l3 crossed with polarizer l2 positioned on the opposite side of thescreen 2 whereby the intelligence of the picture is filtered through as earlier defined.

It should be remarked that polarization of the light beam must be affected after deflection from the member 9 otherwise if attempted before deflection, total polarization will not be affected in the resultant light beam incident upon the face of the modulating screen. Due to the rotary deflecting face it of the member 9, light rays directed from the annular'source 6 would be deflected toward the screen 2 in all planes of polarization not suitable for the purpose. Consequently if the deflecting member 9 is positioned within the tube l, the first polarizer l2 must be positioned likewise.

Fig. 2 illustrates the system in a modified form wherein the deflecting member 9 is positioned externally of the tube l and likewise the first polarizer i2. The opening through the central portion of the members being just large enough to embrace the neck of the tube l. The glass envelope of the tube'l is formed with a shoulder i4 so that the walls at this point transmitting the light into the tube will be suflficiently perpendicular to the incident of the light transmitted, thus preventing loss of light due to refraction and deflection.

It is also obvious that the glass walls of the tube I at this point should be clear and free from deposits or coatings which might obstruct the light passing through into the tube.

The projection lens l which is of the customary type is positioned axially with respect to the optical axis of the system within range of the light intelligence of the picture filtered through'the second polarizerfor projection of the image upon the observation screen 16.

' Various other uses, alterations or modifications within the purview ofthe present invention may become apparent to those skilled in the art and it is desired that any and all modifications be considered except as limited by the hereinafter a light modulating screen with light transmission characteristics, means for generating an electron scanning beam to store modulated impressions upon the face of said screen, the optical axis of said scanning beam perpendicular with respect to the plane of said screen, optical means provided for directing a beam of light to the scanned face of said screen substantially optically coaxial with respect to said scanning means, said optical means including an annular source of light circumscribing a predetermined area centered by said optical axis,and in close proximity of said scanning means, a light reflecting member positioned centrally within said area and within range of said source to reflect the light directed from said source in the form of a beam to the scanned face of said screen, an annular light condensing lens disposed between said source and said member to direct the light from said source to the reflecting face of said member, a projection lens positioned axially with respect to the system and posteriorly to said screen to project the light intelligence of the picture upon an observation screen, the reflecting face of said member in the form of a irustum of a hollow cone with the small base opening sufiiciently large as to permit free action of the electron scanning beam passin through to said screen,

2. A television image projection system including a cathode ray tube having positioned therein a light modulating screen with piezzoelectric and light transmission properties, means for generating an electron scanning beam to store modulated electro-static charges upon the face of said screen, the optical axis of said scanning beam perpendicular with respect to the plane of said screen, means provided for directme a, beam of polarized light to the scanned face of said screen substantially optically coaxial with respect to said scanning means, said means including an annular source of light circumscribing a predetermined area centered by said optical axis and in close proximity of said scanning means, a light reflecting member positioned centrally within said area and within range of said source, an annular light condensing lens disposed between said source and said memher to direct the light from said source to the reflecting face of said member, the reflecting face of said member in the form of a frustum of a hollow cone facing toward said screen to reflect the light directed from said source in the form of a beam to the scanned face of said screen, a light polarizing screen disposed in the path of said light beam closely adjacent to said reflecting member between said member and said modulating screen, an opening provided through the central portion of said polarizing screen sufliciently large as to permit free action of the electron scanning beam passing freely through the hollow portion of said reflecting member to said modulating screen, a second crossed polarizing screen disposed in the path of said light beam posteriorly to said modulating screen to analyze the light intelligence of the picture transmitted thereto and a projection lens positioned axially with respect to the system and posteriorly to said second crossed polarizing screen to project the light intelligence of the picture upon an observation screen.

HAROLD P. PROSSER. 

